Arrangement for eliminating parastic waves



April 13, 1965 L. KIRCHGESSNER ARRANGEMENT FOR ELIMINATING PARASITIC WAVES Filed May 31, 1961 infr 1.

INVENTOE United States Patent 3,178,661 ARRANGEMENT FOR ELIMWATWG PARASETEG WAVEd Leo Kirchgessner, Stuttgart, Germany, assiguor to Robert Bosch G.m.b.I-I., Stuttgart, Germany Filed May 31, 1961, Ser. No. 113,949 Claims priority, application Germany, June 4, i950, a 58,122 11 Claims. (Cl. 333--79) The present invention concerns an arrangement for filtering out high frequency parasitic waves from an electric circuit, and more particularly suitable for an electric circuit connecting a source of electric energy, e.g. a generator, with at least one consumer of such energy, in which case the arrangement according to the invention serves to prevent high frequency parasitic waves developing at some point of origin in the circuit from reaching the consumer.

On account of the establishment of continuously expanding frequency ranges in the field of communications and similar fields of high frequency transmission, the devices used for filtering and for interference elimination serving to prevent parasitic waves from entering receiver devices are faced with tasks which demand correspondingly increasing efficiency and performance. It is not sufficient anymore to eliminate parasitic waves that might interfere with broadcasting frequency bands. It is also necessary to deal similarly with transmissions in the range of television frequency bands and to assure an interference-free reception of the television transmissions. certainly within the realm of probability that in the not too distant future the demand for interference-free reception of all kinds of Wireless radio and television transmission will force those skilled in the art to deal with a frequency range from .1 to 1000 mc./s.

It has been found that conventional devices which weaken high frequency energy by means of voltage dividing or which convert such high frequency energy by suitable means e.g. high resistivity resistors into heat, are not capable of dealing with such expanded conditions.

It is therefore a main object of this invention to provide for an arrangement for preventing high frequency parasitic waves originating somewhere in an electric circuit from reaching another point of the circuit where such parasitic waves are undesirable.

It is another object of this invention to provide for an arrangement of the type set forth which is extremely simple in its construction, reliable in its performance and comparatively inexpensive.

With above objects in view the invention provides in an electrical circuit connecting a source of electric energy with at least one consumer of such energy an arrangement for preventing high frequency parasitic Waves developing at some point of origin in the circuit from reaching the consumer, and comprising a quadripole located in said circuit between the point of origin of the high frequency parasitic waves and the consumer and having character istics relative to the adjoining portion of the circuit resulting in reflection of said parasitic high frequency waves.

A typical example of an electrical circuit where the application of the arrangement according to the invention is highly desirable is a circuit furnished by a generator and containing switch means or other devices eg spark plugs as in the electrical circuit of a motor vehicle, whereby high frequency parasitic waves are produced.

The above mentioned result can be attained egg. by means of a quadripole whose characteristic surge impedance differs greatly from that existing in the adjoining portion or portions of the circuit, the just mentioned difference being such that the characteristic impedance of the quadripole is considerably larger or considerably smaller than that of the corresponding portion of the circuit.

It is "ice portion having the characteristic impedance Z is determined by the equation This equation is to be interpreted in such a manner that the reflection is the greater, the greater is the difference between the two characteristic impedances. If for instance the one characteristic impedance is and the other impedance is 1, then the reflection amounts to 98% which means that only 2% of the interfering high frequency parasitic wave energy passes from the line portion with the characteristic impedance Z into the line portion with the characteristic impedance Z If this second line portion consists of a quadripole inserted into the circuit as a filtering or selective element, then the interference voltage which was reduced to 2% upon its entering the quadripole is again reduced in the same manner upon its emerging from the quadripole on account of the sudden change of characteristic impedance at this transition from one line portion to another one. Consequently only .04% of the original parasitic wave voltage, which may have its origin in a generator arrangement, will pass into the line portion connected with the out-put end of the quadripole.

For instance, in the ignition installation cooperating with an internal combustion engine the main source of parasitic waves is the spark passing between the electrode points of the spark plugs. The high frequency parasitic waves originating at this point travel via the central electrode of the spark plug to the spark plug cable which has a characteristic surge impedance of about 200 ohms. In accordance with the invention a quadripole having a very high characteristic impedance is inserted between the point of origin of the parasitic waves, i.e., the spark plug, and the spark plug cable. In this case a suitable quadripole may be a coiled conductor surrounded by a metal sleeve constituting the outer conductor of the quadripole. The characteristic surge impedance of such a quad-ripole is proportional to the number of turns per unit length of the coiled conductor. Consequently, the coiled conductor must have a large number of turns if its characteristic surge impedance is to be large and if a substantial refiection of the parasitic waves is to be attained thereby.

However, the quadripoles suitable for dealing with the object of this invention may also have other forms of construction as will be described further below.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its. method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is the side view, partially in axial cross section, of a spark plug cable terminal adapted to be attached to a spark plug, and containing a coiled conductor and a surrounding metal sleeve;

FIG. 2 illustrates in perspective view, partially broken, a strip-type attenuating quadripole;

FIG. 3 illustrates, partially in axial section, a co-axial type quadripole; and

PEG. 4 is a schematic circuit diagram of a lighting installation as conventionally used in motor vehicles, and including a quadripole according to FIG. 3.

Referring now to FIG. 1, a spark plug cable terminal suitable to be clipped on the end of a spark plug cornprises a sleeve 10 made of synthetic resin which is surrounded by a metal sleeve 11 which is resilient at one end and formed to be frictionally attached to the end of a spark plug. Within the insulating sleeve a quadripole according to the invention is arranged in the following manner. A coiled conductor 12 is wound about an insulating core, preferably of ceramic material having a diameter of about 4 mm. which carries at either end of a terminal cap 13 connected with the end, respectively, of the coil 12, and equipped with terminal contacts 14 and 15. The contact terminal 14 is adapted to make contact with the central terminal of the spark plug while the contact member 15 having a threaded end, as shown, is adapted to be inserted into the core of the spark plug cable. The coil 12 has a length of about 16 mm. between the terminal caps 13 and comprises 650 turns of a copper wire having a diameter of .02 mm. and a resistance of 450 ohms. The whole quadripole assembly is mounted within the insulating sleeve 10 by the introduction of cast synthetic insulating material 16 in such a manner that no air is enclosed between the quadripole and the sleeve 10.

In view of a diameter of the coil 12 amounting to 4 mm. and an inner diameter of the metal sleeve 11 amounting to 13 mm., and further in view of the insulating material 10, It? having a dielectric constant of about 6, the characteristic surge impedance of the thus formed quadripole arrangement amounts to 9600 ohms. Of course, it is to be assumed that the metal sleeve 11 is grounded in some suitable manner, not shown, but conventional. Assuming now that the characteristic surge impedance of the circuit portion located within the spark plug amounts to ohms the arrangement will have a reflection factor of 98.75% so that at the utmost 1.25% of the parasitic wave voltage emanating from the spark will pass into the quadripole. The high frequency parasitic wave is again reduced, upon its emerging from the quadripole and passing into the spark plug cable, to only 1.25% of its value appearing within the quadripole, so that all told only about .015 of the parasitic high frequency voltage emanating from the spark can pass into the circuit portions beyond the output terminal of the quadripole.

It is to be noted that the above calculated characteristic impedance is not depending upon the prevailing frequency. The filtering effect is only limited by its geometrical dimensions. A spark plug cable terminal containing an attenuating quadripole as described and illustrated is capable to eliminate all parasitic waves in the range from about 10 to 500 mc./s.

The upper limit depends in this case upon the mean diameter of the co-axial outer conductor. On the other hand, the lower limit can be shifted by increasing the length of the coiled wire of the coil 12, or by using as a core for the coil conductor a ferrite core instead of a ceramic core. By using a ferrite core with a relative permeability of about 9 and having a length of 5 cm. parasitic waves in the frequency range from 1 to 500 mc./s. can be eliminated. The ohmic resistance of such an attenuation member is less than 1500 ohms.

In order to avoid standing waves in the lower frequency ranges it is advisable to provide the attenuation quadripole with ohmic, magnetic or dielectric loss characteristics in such a manner that the parasitic Wave energy reflected at the output terminal of the quadripole is practically completely consumed before it has returned to the quadripole input terminal. In this manner the filtering effect of the quadripole can be greatly improved.

In the above described embodiment which is only one example of carrying out the invention, the reflection of the parasitic waves is caused by the fact that the quadripole inserted in a circuit has a very great characteristic surge impedance as compared with that of the adjoining portion or portions of the circuit. However, the same effect can be attained also by means of a quadripole having an extremely low characteristic impedance. In this case also a high frequency wave arriving through a circuit portion having a relatively high ohmic resistance (characteristic surge impedance of e.g. 100 ohms) is reflected the first time upon its transition into the quadripole and a second time before it can emerge from the quadripole.

In a modification of the invention, differing from the example illustrated by FIG. 1, circuit components having such low characteristic impedances may be constructed e.g. as a strip-type or as a special type of co-axial conductor. In a strip-type conductor as illustrated by FIG. 2 the conductor which carries the operating current and a high frequency parasitic current consists of a wide strip 20 which is confronted by a second strip 21 of the same width serving as return conductor. The spacing between the two strips 20 and 21 consists of a thin layer 22 of dielectric material having as high a dielectric constant as possible. The characteristic surge impedance of a striptype conductor arrangement of this sort depends mainly upon the width of the two conductor strips and upon the thickness of the dielectric material therebetween and its dielectric constant. This impedance can easily be predetermined to be of the order of .02 ohm. If a strip-type conductor arrangement of his type is inserted as an attenuation quadripole in a circuit having a characteristic surge impendance of 60 ohms, then the ratio between the characteristic impedances of the regular circuit and of the quadripole is 113000 so that the reflection factor is 99.9%. Since in a strip-type conductor arrangement of this type comparatively large areas and cross sections but only small spacings prevail, an arrangement of this type is particularly suitable for eliminating parasitic waves in low voltage networks carrying comparatively large operative currents.

The required length of a strip-type conductor arrangement of the above mentioned type is to be determined in consideration of the lower limit frequencies at which a sufiicient elimination of parasitic waves is desired. Consequently, these strip-type conductor arrangements cannot be in a straight extending position, it is rather advisable to wind them, similar to the construction of a wound condenser, as a coil having terminals at both ends for being connected into a circuit. It is of importance that the current which is to be freed of parasitic waves flows through the entire length of the quadripole constituted by the strip-type conductor arrangement.

A further modification of the invention is illustrated by FIG. 3 in which case a particularly suitable attenuation quadripole consists of a co-axial conductor arrangement. In this case a conductor 30 which carries the current that is disturbed by parasitic waves, is surrounded by a thin ceramic layer 31, e.g. made of barium titanate having a dielectric constant of 10,000, and to this ceramic layer a thin silver coating 32 is applied either by vapor deposition or by fusing. The characteristic surge impedance of a filtering quadripole of this type, assuming a diameter of the conductor 30 of 6 mm. carrying amperes, and a layer of barium titanate of .5 mm. thickness, is about .1 ohm, and the reflection factor of such a quadripole inserted into a circuit having generally a characteristic surge impedance of 60 ohms amounts to 99.6%.

F or a lower limit frequency of 3.5 mc./s. the length of a co-axial conductor arrangement of the above described type is 20 cm. Consequently the arrangement is kept within the dimensional limits of conventional interference eliminators, however it is very much simpler in its construction and has a much smaller volume or space requirement than those.

By way of example, attenuation quadripoles of the just described type may find excellent use within the network of a lighting installation of motor vehicles as is illustrated by FIG. 4 In this example the armature 35 of a direct current generator delivers 600 watts at a normal output voltage of 12 volts, the exciter winding being indicated at 36 and a series resistance connected with the winding 36 is indicated by 37. A conventional regulator switch cooperating with the generator arrangement comprises regulator contacts 38, 39, 40, a voltage coil 41, a current coil 42 and a pair of main switch contacts 43, 44. When the last mentioned switch contacts 43, 44 are in conductive position a current flows from the generator 35 to a storage battery 45 but passes on its way through an attenuation quadripole 46 connected between the switch contact 44 and the battery 45 and formed as a co-axial conductor arrangement according to FIG. 3. Of course, the outer layer 32 is grounded. The length of the quadipole 46 is 20 cm. In this manner the usually rather long conductor of the circuit between the switch arrangement 43, 44 and the battery 45 is entirely freed by the quadripole 46 of disturbing high frequency parasitic waves which are usually produced by circuit opening and circuit closing sparks between the contacts 43 and 44 or between the regulator contacts 33, 39 and 40. In an arrangement of this type the filtering effect reaches far into the range of 1000 rnc./s. frequencies.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of an arrangement for eliminating high frequency parasitic waves differing from the types described above.

While the invention has been illustrated and described as embodied in quadripole arrangement for eliminating high frequency parasitic waves from a circuit, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A spark plug cable terminal fixture adapted to be attached to a spark plug and to a cable having a predetermined surge impedance, comprising, in combination, a central conductor member having a predetermined impedance and connectable with the spark plug cable, and an outer metal shell connectable to ground and separated from said central conductor by a layer of dielectric material, said combination of central conductor, outer shell and dielectric layer constituting a quadripole having also a predetermined surge impedance, one of said surge impedances being so small a fraction of the other surge impedance that said quadripole has a reflection factor of at least 90% so as to reflect toward said spark plug at least at one end of said quadripole parasitic high frequency waves originating in the spark plug during its operation and being substantially within the frequency range from 1 to 1000 mc./s.

2. A spark plug cable terminal fixture as claimed in claim 1, wherein said quadripole has a characteristic surge impedance of at least 1,000 ohms.

3. A spark plug cable terminal fixture as claimed in claim 1, wherein said quadripole has a characteristic surge impedance of at least 5,000 ohms.

4. A spark plug cable terminal fixture as claimed in claim 1, wherein said layer of dielectric material com prises a sleeve of insulating material surrounding said wire coil, and cast synthetic material filling completely the space between said wire coil and the inner face of said sleeve of insulating material.

5. In an electric circuit, in combination, a source means of electric energy developing also high-frequency parasitic waves; a consumer means; a wave reflector means con- 6 nested in series between said source means and said consumer means, said wave reflector means including a quadripole having a predetermined surge impedance; and at least one circuit portion connected between said wave reflector means and one of said other means and having also a predetermined surge impedance, one of said surge impedances being so small a fraction of the other surge impedance that the reflection factor of said wave reflector means including said quadripole is at least so that parasitic high frequency waves substantially within the frequency range from 1 to 1000 rnc./ s. are reflected toward said source means at least at one end of said quadripole, whereby said parasitic waves are substantially prevented from reaching said consumer.

6. An arrangement as claimed in claim 5, wherein said quadripole consists of a co-axial conductor arrangement having an inner conductor connected in the circuit, an outer concentric conductor and a dielectric layer separating said inner and outer conductors.

7. An arrangement as claimed in claim 5, wherein said quadripole consists of a strip-type conductor arrangement having a first conductor strip and a second conductor strip parallel therewith, and a layer of dielectric material separating said first and second conductors from each other.

8. A spark plug cable terminal fixture adapted to be attached to a spark plug and to a spark plug cable, comprising, in combination, a central conductor member including a core of ferrite, a wire coil wound about said core and connectable at one end to the spark plug and at its other end to the cable; a layer of insulating material surrounding said central conductor member; and an outer metal shell connectable to ground and separated from said central conductor member by said layer of insulating material, said layer comprising a sleeve of insulating material surrounding said wire coil and cast synthetic material filling completely the space between said wire coil and the inner face of said sleeve, said combination of central conductor, outer shell and dielectric layer constituting a quadripole having a surge impedance greatly differing from that of the spark plug cable to such a great extent that its reflection factor is at least 90% whereby parasitic high frequency waves substantially within the frequency range from 1 to 1000 mc./ s. tending to pass the terminal fixture are reflected.

9. In an electric circuit, in combination, a source means of electric energy developing also high-frequency parasitic waves; a consumer means; a wave reflector means connected in series between said source means and said consumer means, said wave reflector means including a quadripole having a first predetermined surge impedance; and one circuit portion connected between said wave reflector means and said source means and having a second predetermined surge impedance, and another circuit portion connected between said wave reflector means and said consumer means and having a third predetermined surge impedance, one of said first and second surge impedances being so small a fraction of the other one thereof, and one of said first and third surge impedances being so small a fraction of the other one thereof that said wave reflector means including said quadripole as a reflection factor of at least 90% so that parasitic high frequency waves substantially within the frequency range from 1 to 1000 mc./s. are reflected toward said source means at both ends of said quadripole, whereby said parasitic waves are substantially prevented from reaching said consumer.

10. In an electric circuit, in combination, a source means of electric energy developing also high frequency parasitic waves; a consumer means; a circuit connecting said source means and said consumer means; a wave reflector means connected in said circuit in series between said source means and said consumer means so as to form one circuit portion between itself and said source means and another circuit portion between itself and said consumer means, each of said circuit portions having a predetermined surge impedance, said wave reflector means comprising a central conductor member including a core of ferrite, a wire coil wound about said core and connected at one end to the said first circuit portion and at its other end to said second circuit portion, a layer of insulating material surrounding said central conductor member, an outer metal shell connectable to ground and separated from said central conductor member by said layer of insulating material, said layer comprising a sleeve of insulating material surrounding said wire coil and case synthetic material filling completely the space between said wire coil and the inner face of said sleeve, said combination of central conductor, outer shell and dielectric layer constituting a quadripole having also a predetermined surge impedance; the predetermined surge impedance of said quadripole differing from said predetermined surge impedance of one of said circuit portions to such an extent that the reflection factor of said wave reflector means including said quadripole is at least 90% so that parasitic high frequency waves substantially within the frequency range from 1 to 1000 mc./ s. are reflected toward said source means at least at one end of said quadripole, whereby said parasitic waves are substantially prevented from reaching said consumer means.

11. In an electric circuit, in combination, a source means of electric energy developing also high frequency parasitic waves; a consumer means; a circuit connecting said source means and said consumer means; a wave reflector means connected in said circuit in series between said source means and said consumer means so as to form one circuit portion between itself and said source means and another circuit portion between itself and said consumer means, each of said circuit portions having a predetermined surge impedance, said wave reflector means including a central conductor member connected at one end to said one circuit portion and at its other end to said other circuit portion; a sleeve of dielectric material surrounding said central conductor member and an outer metal shell connectable to ground said central conductor member, outer shell and dielectric sleeve constituting a quadripole having also a predetermined surge impedance which dilfers from said predetermined surge impedances of one of said circuit portions to such an extent that the reflection factor of said wave reflector means including said qu-adripole is at least 90% so that parasitic high frequency waves substantially within the frequency range from 1 to 1000 mc./s. are reflected toward said source means at least at one end of said quadripole, whereby said parasitic waves are substantially prevented from reaching said consumer means.

References Cited by the Examiner UNITED STATES PATENTS 1,645,643 10/27 Crook 3158.5 2,322,773 6/43 Peters 174-119 2,376,101 5/45 Tyzzer 333-l2 2,427,247 9/47 Wilkinson 33331 2,565,093 8/51 Robinson et a1. 333-12 2,669,695 2/54 Bird 333-12 3,004,229 10/61 Stearns 333-84 3,024,430 3/62 Zanntes 333-73 3,041,498 6/62 Fontaine 315-85 FOREIGN PATENTS 229,925 11/43 Switzerland. 939,611 10/63 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner. 

1. A SPARK PLUG CABLE TERMINAL FIXTURE ADAPTED TO BE ATTACHED TO A SPARK PLUG AND TO A CABLE HAVING A PREDETERMINED SURGE IMPEDANCE, COMPRISING, IN COMBINATION, A CENTRAL CONDUCTOR MEMBER HAVING A PREDETERMINED IMPEDANCE AND CONNECTABLE WITH THE SPARK PLUG CABLE, AND AN OUTER METAL SHELL CONNECTABLE TO GROUND AND SEPARATED FROM SAID CENTRAL CONDUCTOR BY A LAYER OF DIELECTRIC MATERIAL, SAID COMBINATION OF CENTRAL CONDUCTOR, OUTER SHELL AND DIELECTRIC LAYER CONSTITUTING A QUADRIPOLE HAVING ALSO A PREDETERMINED SURGE IMPEDANCE, ONE OF SAID SURGE IMPEDANCE BEING SO SMALL A FRACTION OF THE OTHER SURGE IMPEDANCE THAT SAID QUADRIPOLE HAS A REFLECTION FACTOR OF AT LEAST 90% SO AS TO REFLECT TOWARD SAID SPARK PLUG AT LEAST AT ONE END OF SAID QUADRIPOLE PARASITIC HIGH FREQUENCY WAVES ORIGINATING IN THE SPARK PLUG DURING ITS OPERATION AND BEING SUBSTANTIALLY WITHIN THE FREQUENCY RANGE FROM 1 TO 1000 MC./S. 